The Sinn Féin leader said "judges make mistakes" and repeatedly dodged questions on whether he was undermining the High Court and the Supreme Court who both ruled that Murphy's tax evasion case should be held in a non-jury setting.

After being asked four times whether those two courts treated the former IRA godfather unfairly, Mr Adams said: "That's a matter for them."

He also fudged queries as to how gangsters such as John Gilligan and the Dundons would be dealt with if, as Sinn Féin proposes, the Special Criminal Court was abolished.

The first public hint of unease within Sinn Féin over the Murphy case emerged last night when their justice spokesman Padraig Mac Lochlainn declined to tell the Irish Independent whether he considers Murphy 'a good republican'.

"I don't know Tom Murphy. I have never met him in my life. But I noted the comments of Gerry Adams and Martin McGuinness in relation to Tom Murphy," he said.

In an extraordinary performance on the plinth at Leinster House, Mr Adams appeared not to know that Murphy and his two brothers had agreed to surrender €630,000 that was found on family lands in Louth to the State following a Criminal Assets Bureau investigation.

"He has contested all of this. Is it his property? Can you stand that up? I don't know whose property it is," Mr Adams told journalists.

Amazingly, the Louth TD claimed he can't remember the last time he spoke with Murphy, despite repeatedly coming to his defence in recent days. He claimed not to know if Murphy was the IRA's chief of staff at any stage and said he "doubts" if he has donated any money to the Sinn Féin party.

"I know this man through the engagement in the peace process, winning support for a series of propositions which our leadership brought forward," he said.

Mr Adams could only explain his defence of a tax cheat by saying he was against "draconian laws" that saw people tried in the Special Criminal Court.

"I think judges can make mistakes. The certainty for citizens is that we are tried by our peers. That's the safest process and juries can make mistakes as well," he said.

He went on to say that he did not believe people who were involved in the IRA were criminals.

Asked whether everybody in Sinn Féin was comfortable with his public utterances, Mr Adams said "any talks about splits in Sinn Féin or people being uneasy about this is just wishful thinking".

However, his justice spokesman Padraig Mac Lochlainn was less forceful than his party leader when he spoke about the case for the first time last night.

He told the Irish Independent he had never met Murphy.

"I don't care if somebody was in the IRA in the past. Everybody who has been involved in any type of criminal activity should be pursued vigorously," he said.

"I don't know if Tom Murphy paid his taxes. If he didn't, he must [face the] full rigours of the law."

Mr Adams has also openly questioned the decision of the Director of Public Prosecution Claire Loftus to refer the case to the Special Criminal Court, but Mr Mac Lochlainn said: "My quarrel is not with the DPP. It is with the use of the Special Criminal Court."

Tánaiste Joan Burton reacted to Mr Adams's press conference by describing him as a spokesperson for the IRA.

"I am at a loss to understand why Gerry Adams still references a necessity for the IRA, an organisation which, if we believe him, he has never been a member of, but for which he seems to be a spokesperson and a publicist on every possible occasion."

She added: "I am a republican. Every citizen of this State is a constitutional republican and I actually deplore the name republican being abused by people involved in paramilitarism, crime, murder, extortion and racketeering."

Ms Burton said she would prefer if cases didn't have to be referred to the Special Criminal Court but it was necessary to protect witnesses due to the history of "paramilitaries" and "gangsterism on the border".

"The extent of Thomas Murphy's continued influence over the Sinn Féin organisation and its leaders became very clear when Gerry Adams doubled down in his defence of the convicted tax cheat and actually went one step further than he has in recent days," he said.

"Mr Adams refused to accept the judgment of the Special Criminal Court.

"Then, when confronted with the truth about his bluff on the SCC, namely that the decision to hold the case that was vindicated in the Supreme Court, all Mr Adams could offer was that 'judges make mistakes'."

Mr Collins claimed "every institution in this State is secondary to the internal needs and dynamics of the Sinn Féin project".